[BC] Lat Long question (Answered)

[Tom]

Caveat, though -

The errors may not be trivial in all instances - for example, I 
converted a small-town FM's NAD-27 to NAD-83, and plugged into Google 
earth.  the TX site was well over 600 feet off east; close to the 100 
meter maximum error indicated for conversion between the original NAD-27 
co-ordinates and the revised NAD-83(86).

The offset between the NAD-83 co-ordinates and what you can get from a 
set of GPS readings will be within a meter or so, according to USGS...

 From the previously-linked NADCON site:

"NAD 83 coordinates based on the HPGN/HARN surveys changed approximately 
0.2 to 1.0 meter relative to the original NAD 83 (1986) adjustment. As 
these high accuracy networks have been completed, the horizontal 
geodetic network of each state has been re-adjusted to be consistent 
with its network of A- and B-order control, thus creating a need for 
grids that allow for the transformation from the NAD 83(86) adjustment 
to the new adjusted values. These grids carry the designation 'HPGN' to 
distinguish them from the grids created from the original NAD 83(86) 
adjustment."

NADCON claims a conversion accuracy to within ~12-18 cm for NAD-27 to 
NAD-83, and ~5-6 cm from NAD-83 to HARN - so, maximum possible error 
would be roughly 24 cm - or less than 12 inches off...


RichardBJohnson at comcast.net wrote:
> They are not far off from each other for practical
> purposes, but if you want to make a FCC filing,
> some corrections should occur. Here's the Hammet
> and Edison paper on the subject.
>
> http://www.h-e.com/pdfs/de_sbe94.pdf
>
> Note that most of the surveying in the Northeast
> is awful (read wrong). There are whole towns
> that are not where they purport to be. In fact,
> computerization of property boundaries in the
> 80's disclosed that there is about twice as
> much property (area) owned as actually exists!
> When you hire a surveyor to survey some land,
> they try to reconstruct the original boundaries
> and replace the words with geographical
> coordinates. It isn't easy!
>
> Even the GPS coordinates need to be
> "corrected" because they assume a spherical
> earth with its center of gravity in its center,
> when, in fact it is pear-shaped, with the CG
> displaced off towards the Andes Mountains!
>
> So, unless you are making a FCC filing,
> Google-Earth is close enough with the
> maximum error being 1.3 seconds in
> latitude and 4.4 seconds in longitude.
> Move the Google Cursor see how small
> a distance that is!
>
> --
> Cheers,
> Richard B. Johnson
> Read about my book
> http://www.LymanSchool.org
>
>
>  -------------- Original message ----------------------
> From: "Ronald J. Dot'o Sr." <ron.doto at comcast.net>
>   
>> It appears that Google Earth uses NAD 83.
>>
>> Ron D
>>
>>
>> ----- Original Message ----- 
>> From: "Ronald J. Dot'o Sr." <ron.doto at comcast.net>
>>
>>
>>     
>>> I know that the FCC uses NAD 27 on their applications.  Does anyone 
>>> know which NAD Google Earth and M$ Virtual Earth use when you run the 
>>> curser over a specific point to get a Lat Long readout?
>>>
>>> Ron D
>>>       
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-- 
Tom Spencer
PG-18-25453 (nee' P1-18-48841)
http://radioxtz.com/
Part 15 transmitters on AM 640 and FM 100.1